Soil systems contain a variety of microorganisms including bacteria, fungi and algae. Bacterial populations in soil survive and flourish depending on the availability of nutrients and carbon sources. Aerated soils including topsoil typically have the highest population of bacteria. A level of population for each type of bacteria in soil is defined based on the competition among soil bacteria. Competition may be shifted toward a specific type of bacteria due to changes in the availability of growth requirements as well as changes resulting in the alteration of physical or chemical conditions within the subsurface environment. The addition or natural presence of a carbon source becomes a major element affecting the bacterial diversity in an ecosystem. Fungi live in symbiotic relationships with plants among their roots, feeding on organic materials and assisting plants in water and mineral uptake. A number of genera of algae live both on the soil surface and within the soil, where they produce oxygen used by aerobes and serve as a food source for other microorganisms.
Commercial growers have access to inoculant products that add specific beneficial fungi and bacteria to a soil mix, growing bed or crop. It is reported by some that these microorganisms help prevent disease, increase plants' tolerance to stress and increase their vigor. Some farmers and crop growers have claimed that these products even increase plants' cold tolerance. These products are available as a powder to mix with water and add to soils, or as granular material that is mixed with water and added to soil. Some of these products are mixed with nutrients that also increase the number of existing microorganisms.
In general, bacteria-based products are lower in cost than fungal-based products or enhancers. Both the bacterial products and fungal products are designed to increase nutrient uptake, promote faster root development, and reduce heat, drought and cold stress. These products also stimulate other beneficial soil microorganisms to thrive. Thus, these commercial products increase overall crop health, even those crops grown in soil-less media or in soil that has become exhausted and overworked. However, soil based amendments applied through inoculation methods may not be reliable.